The present invention relates generally to diesel engines with exhaust aftertreatment systems (EATS) and methods of treating exhaust gases from a diesel engine and, more particularly, to such engines and EATS and methods wherein fuel injection and engine exhaust characteristics are varied during regeneration.
Commonly assigned International Application Publication WO2009/100412 and commonly-assigned International Application Publication WO2009/100413, both of which are expressly incorporated by reference, disclose regeneration of diesel particulate filters (DPF) in EATS via NO2 regeneration. So-called “active” NO2 regeneration at temperatures usually in the range of 450° C.-550° C., which are above conventional passive NO2 regeneration temperature ranges and below conventional active O2 regeneration temperature ranges, produces encouraging results when compared to either conventional passive NO2 or conventional active O2 regeneration. However, under many conditions, particularly when the engine and EATS is used in vehicular, over-the-road transient operations, fuel injected via a so-called seventh injector to heat a DPF to temperatures desired for active NO2 regeneration can cause hydrocarbon slip through a diesel oxidation catalyst (DOC) upstream of the DPF, which can inhibit NO2 recycling that is desirable for the active NO2 regeneration.
It is desirable to provide a method of treating exhaust gases and an engine and exhaust aftertreatment system that permits DPF regeneration, particular performing active NO2 regeneration, under conditions that can reduce the risk of hydrocarbon slip past a DOC or a DPF. It is also desirable to provide a method of treating exhaust gases and an engine and exhaust aftertreatment system that permits performing effective DPF regeneration, particular performing active NO2 regeneration, under conditions that reduce risk of runaway regeneration or other thermal damage to a DPF or an SCR.
According to an aspect of the present invention, a method of treating exhaust gases from a diesel engine comprises operating the engine and passing exhaust gases through a diesel particulate filter (DPF), operating the engine to obtain a first set of exhaust characteristics and injecting fuel upstream of the DPF at a first rate of injection until at least one condition is attained, and after the at least one condition is attained, reducing a rate of fuel injection and operating the engine to obtain a second set of exhaust characteristics so that regeneration of the DPF occurs, at least one characteristic of the first and second sets of characteristics being different.
According to another aspect of the present invention, a diesel engine and exhaust aftertreatment system comprises a diesel engine adapted to be operated to attain at least two different sets of exhaust characteristics, a diesel particulate filter (DPF) downstream of the engine, a fuel injector downstream of the engine and upstream of the DPF, and a controller arranged to control operation of the engine to obtain a first set of exhaust characteristics and to control the fuel injector to inject fuel upstream of the DPF at a first rate of injection until at least one condition is attained, and, after the at least one condition is attained, to control the fuel injector so that a rate of fuel injection is reduced and to control operation of the engine to obtain a second set of exhaust characteristics so that regeneration of the DPF occurs, at least one characteristic of the first and second sets of characteristics being different.